Aqueous cleaning processes are a mainstay of conventional domestic and industrial textile fabric cleaning methods. On the assumption that the desired level of cleaning is achieved, the efficacy of such conventional processes is usually characterized by their levels of consumption of energy, water and detergent. In general, the lower the requirements with regard to these three components, the more efficient the washing process is deemed. The downstream effect of reduced water and detergent consumption is also significant, as this minimizes the need for disposal of aqueous effluent, which is both extremely costly and detrimental to the environment.
Conventional washing processes involve aqueous submersion of fabrics followed by soil removal, aqueous soil suspension, and water rinsing. In general, within practical limits, the higher the level of energy (or temperature), water and detergent which is used, the better the cleaning. The key issue, however, concerns water consumption, as this sets the energy requirements (in order to heat the wash water), and the detergent dosage (to achieve the desired detergent concentration). In addition, the water usage level defines the mechanical action of the process on the fabric, which is another important performance parameter; this is the agitation of the cloth surface during washing, which plays a key role in releasing embedded soil. In aqueous processes, such mechanical action is provided by the water usage level in combination with the drum design for any particular washing machine. In general terms, it is found that the higher the water level in the drum, the better the mechanical action. Hence, there is a dichotomy created by the desire to improve overall process efficiency (i.e. reduce energy, water and detergent consumption), and the need for efficient mechanical action in the wash.
Various different approaches to the development of new cleaning technologies have been reported in the prior art, including methods which rely on electrolytic cleaning or plasma cleaning, in addition to approaches which are based on ozone technology, ultrasonic technology or steam technology. Thus, for example, WO2009/021919 teaches a fabric cleaning and disinfection process which utilizes UV-produced ozone along with plasma. An alternative technology involves cold water washing in the presence of specified enzymes, whilst a further approach which is particularly favored relies on air-wash technology and, for example, is disclosed in US2009/0090138. In addition, various carbon dioxide cleaning technologies have been developed, such as the methods using ester additives and dense phase gas treatments which are described in U.S. Pat. No. 7,481,893 and US2008/0223406, although such methods generally find greater applicability in the field of dry cleaning. Many of these technologies are, however, technically very complex.
In the light of the challenges which are associated with aqueous washing processes, the present applicant has previously devised a new approach to the problem that allows the deficiencies demonstrated by the methods of the prior art to be mitigated or overcome. The method which is provided may significantly reduce or eliminate the requirement for the use of large volumes of water, but is still capable of providing an efficient means of cleaning and stain removal from textile fabric substrates, whilst also yielding economic and environmental benefits.
Thus, in WO2007/128962 there is disclosed a method and formulation for cleaning a soiled substrate, the method comprising the treatment of the moistened substrate with a formulation comprising a multiplicity of polymeric particles, wherein the formulation is free of organic solvents. The substrate may be wetted so as to achieve a substrate to water ratio of between 1:0.1 to 1:5 w/w, and optionally, the formulation may additionally comprise at least one cleaning material, which typically comprises a surfactant, which most preferably has detergent properties. The substrate may comprise a textile fiber. The polymeric particles may, for example, comprise particles of polyamides, polyesters, polyalkenes, polyurethanes or their copolymers, a particular example being nylon beads.
The use of this cleaning method, however, presents a requirement for the polymeric particles (such as nylon beads) to be efficiently separated from the cleaned substrate at the conclusion of the cleaning operation, and this issue was initially addressed in WO2010/094959, which provides a novel design of cleaning apparatus requiring the use of two internal drums capable of independent rotation, and which finds application in both industrial and domestic cleaning processes.
With a view to providing a simpler, more economical means for addressing the problem of efficient separation of the cleaning beads (polymeric particles) from the substrate at the conclusion of the cleaning process, however, a further apparatus is disclosed in WO2011/064581. The apparatus of WO2011/064581, which finds application in both industrial and domestic cleaning processes, comprises a perforated drum and a removable outer drum skin which is adapted to prevent the ingress or egress of fluids and solid particulate matter (e.g. polymeric particles) from the interior of the drum. The cleaning method requires attachment of the outer skin to the drum during a first wash cycle, after which the skin is removed prior to operating a second wash cycle, following which the cleaned substrate is removed from the drum.
The apparatus and method of WO2011/064581 is found to be extremely effective in successfully cleaning substrates, but the requirement for the attachment and removal of the outer skin detracts from the overall efficiency of the process and the present applicant has, therefore, sought to address this aspect of the cleaning operation and to provide a process wherein this procedural step is no longer necessary. Thus, by providing for continuous circulation of the cleaning beads (solid particulate material, such as polymeric particles) during the cleaning process, it has been found possible to dispense with the requirement for the provision of an outer skin.
Thus, in WO2011/098815, the present applicant provided an apparatus for use in the cleaning of soiled substrates, the apparatus comprising housing means having a first upper chamber with a rotatably mounted cylindrical cage mounted therein and a second lower chamber located beneath the cylindrical cage, and additionally comprising at least one recirculation means, access means, pumping means and a multiplicity of delivery means, wherein the rotatably mounted cylindrical cage comprises a drum having perforated side walls where up to 60% of the surface area of the side walls comprises perforations comprising holes having a diameter of no greater than 25.0 mm.
The apparatus of WO2011/098815 is used for the cleaning of soiled substrates by means of methods which comprise the treatment of the substrates with formulations comprising solid particulate cleaning material and wash water, the methods typically comprising the steps of:                (a) introducing solid particulate cleaning material and water into the lower chamber of the apparatus;        (b) agitating and heating the solid particulate cleaning material and water;        (c) loading at least one soiled substrate into the rotatably mounted cylindrical cage via the access means;        (d) closing the access means so as to provide a substantially sealed system;        (e) introducing the solid particulate cleaning material and water into the rotatably mounted cylindrical cage;        (f) operating the apparatus for a wash cycle, wherein the rotatably mounted cylindrical cage is caused to rotate and wherein fluids and solid particulate cleaning material are caused to fall through perforations in the rotatably mounted cylindrical cage into the lower chamber in a controlled manner;        (g) operating the pumping means so as to transfer fresh solid particulate cleaning material and recycle used solid particulate cleaning material to separating means;        (h) operating control means so as to add the fresh and recycled solid particulate cleaning material to the rotatably mounted cylindrical cage in a controlled manner; and        (i) continuing with steps (f), (g) and (h) as required to effect cleaning of the soiled substrate.        
As outlined above, the apparatus of WO2011/098815 therefore includes features to introduce solid particulate cleaning material into the rotatably mounted cylindrical cage and also comprises at least one recirculation means to facilitate recirculation of said solid particulate material for its re-use in cleaning operations. In addition, the apparatus of WO2011/098815 can include ducting comprising separating means for separating the solid particulate material from water and control means adapted to control entry of the solid particulate material into the cylindrical cage. In one disclosed embodiment, the separating means comprises a rigid filter material such as wire mesh located in a receptor vessel above the cylindrical cage, and the control means comprises a valve located in feeder means, preferably in the form of a feed tube attached to the receptor vessel, and connected to the cage.
Although the apparatus disclosed in WO2011/098815 provided considerable improvements for the cleaning of soiled substrates with formulations comprising solid particulate cleaning material and wash water, there remain several drawbacks.
One problem which may occur is an accumulation of solid particulate material within a pumping device used for the circulation of the solid particulate material. Such accumulation can potentially render the pumping device inoperative until such accumulation is removed, which may require the intervention of a skilled operative.
In particular, the pumping device of the prior art may be located in, or in direct communication with, a lowermost part of a collecting space for the solid particulate material, such as a sump. The collecting space is configured to collect the solid particulate material at certain stages of, or times in, the wash process when such solid particulate material is not needed in the cylindrical cage. The collecting space is configured so that a mass or body of the solid particulate material may accumulate at the lowermost part thereof. When required for use, the solid particulate material is transferred from the collecting space by a pumping means. However, the solid particulate material may enter the pumping device and form a mass or body therein. The formation of such mass or body within the pumping device may be encouraged by the vibrations of the apparatus which occur during the cleaning cycle. Such vibrations encourage entry of the solid particulate material into the pumping device, notably when the pumping device is not in operation and can further encourage some compaction of the mass of solid particulate material within the pumping device. The compacted mass of solid particulate material can prevent the pumping device form starting when required. Effectively, a blockage in the pumping device is formed which must be displaced, such as by operator intervention, before the pumping device can be started for transferring the solid particulate material from the collecting space.
It has further been observed in apparatus of the prior art that variations in relative amounts of solid particulate material and liquid (water or water and detergent for example) exiting the pumping device can occur. This means that a desired ratio of solid particulate material and liquid in the cleaning volume might not be achieved, for optimization of the cleaning procedure. The inventors have appreciated that such variations may be attributable to factors such as the quantity of fluid in the collecting volume at any given time and the volume and density of packing of the solid particulate material in the collecting volume (at least in proximity to the pumping device) at any given time.
In some embodiments, the present disclosure seeks to provide a cleaning apparatus for use in the cleaning of soiled substrates with a solid particulate material that can ameliorate or overcome above-noted problems associated with the prior art.
Particularly, there is desired an apparatus and method for the cleaning of soiled substrates which can alleviate problems associated with the accumulation of solid particulate material in, or in proximity to, a pumping device used for circulation of the solid particulate material.
Also there is desired an apparatus and method for cleaning substrates in which a substantially constant ratio of solid particulate material and fluid exiting the pumping device can be achieved.